【Unity】アバターをまとめて1SetPassにする ref: http://qiita.com/iwashihead/items/e36fd5578643f8e146a9

file0.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;

public class RuntimeCharacterAtlasTest : MonoBehaviour
{
    public Texture2D BodyTex;
    public Texture2D HairTex;
    public Texture2D EyeTex;

    public Texture2D AtlasTex;
    public Material AtlasMaterial;

    public SkinnedMeshRenderer[] BodyMeshs;
    public SkinnedMeshRenderer[] HairMeshs;
    public SkinnedMeshRenderer[] EyeMeshs;

    public Rect[] Rects;

    public IEnumerator Start()
    {
        // AtlasTextureの生成.
        AtlasTex = new Texture2D(2048, 2048);

        // Unity起動直後は正確に計測できないのでしばらく待つ.
        yield return new WaitForSeconds(3f);

        // ~~~~~計測開始~~~~~
        Stopwatch sw = new Stopwatch();
        sw.Start();

        // TextureのAtlas化を行う.
        // Rects に各Textureの領域情報が返ってくる、順番は引数のTexture配列と同じ.
        Rects = AtlasTex.PackTextures(new [] {BodyTex, HairTex, EyeTex}, 2);

        // Atlas用のMaterialにAtlasTextureを割り当てる
        AtlasMaterial.mainTexture = AtlasTex;

        // PackTextureに渡した順番でUVを更新
        ApplyUVAndMaterial(BodyMeshs, Rects[0], AtlasMaterial);
        ApplyUVAndMaterial(HairMeshs, Rects[1], AtlasMaterial);
        ApplyUVAndMaterial(EyeMeshs, Rects[2], AtlasMaterial);

        // ~~~~~計測終了~~~~~
        sw.Stop();
        //UnityEngine.Debug.Log("total atlas create time = " + sw.ElapsedTicks + " ticks");
    }

    // UVを更新して、AtlasMaterialを割り当てる
    public void ApplyUVAndMaterial(SkinnedMeshRenderer[] meshs, Rect rect, Material atlasMaterial)
    {
        foreach (var mesh in meshs)
        {
            var uvs = new List<Vector2>();
            // 元のMesh情報を上書きしないように、Instanctiateしてメッシュをコピー
            mesh.sharedMesh = Instantiate(mesh.sharedMesh);
            // 元々のUV情報を取得
            mesh.sharedMesh.GetUVs(0, uvs);
            // Atlasマテリアルを割り当て
            mesh.material = atlasMaterial;

            for (int i = 0; i < uvs.Count; ++i)
            {
                // Atlas化してずれたUVを更新する.
                uvs[i] = new Vector2(uvs[i].x * rect.width + rect.x, uvs[i].y * rect.height + rect.y);
                // 新しいUVを割り当て
                mesh.sharedMesh.SetUVs(0, uvs);
            }
        }
    }
}